The present invention relates to a holes saw and in particular to a rotatable hole saw supported by a mandrel which is inserted in a drill chuck or the like.
Hole saws are widely used to cut circular holes for many applications. Typically a hole saw is cylindrically shaped with cutting teeth at one end and a threaded boss at the other for screwing into a mandrel for rotational operation in a drill.
A pilot drill extends from the centre of the mandrel and through the centre of the hole saw as it is screwed onto the mandrel. As it always protrudes further than the length of the hole saw blade and hence contacts the material to be cut first the pilot drill is the first to cut the hole in the material and acts as the exact centre of the hole saw diameter. This hole then acts as a guide or “pilot” around which the hole saw then concentrically cuts a larger hole.
In a previous application PCT/AU02/011296, whose contents are incorporated by express reference herein, the present applicant disclosed an arrangement whereby a threaded boss is screwed into a hole saw which is then quickly mounted and demounted from a mandrel.
However in very large hole saws, the rotational force developed (or torque required to rotate the hole saw) when operating the mandrel in heavier machinery may strip the thread where the hole saw couples with the boss. This may also be true when cutting through very hard material.
To overcome these problems, in a further application PCT/AU2004/000376, whose contents are also incorporated herein by express reference thereto, there is proposed an apparatus for overcoming the problem of stripping threads by the insertion of two loose pins to engage the boss and saw to avoid driving on the threads.
The problem with this type of arrangement is that it is awkward to assemble the apparatus and use the pins which, when the hole saw is not engaged to the mandrel, are loose and can easily be lost. Farther the hole saw may be somewhat loose on the mandrel when such pins are used, since they are abutting against the mandrel and may separate the mandrel from the boss.
It is an object of the present invention to overcome at least some of the above-mentioned problems or provide the public with a useful alternative.